Question: What makes a black hole so powerful? Why is it strong enough to suck light in?

Iain Bethune answered on 16 Jun 2015:

A black hole occurs when a star become large enough that it’s own gravity causes it to collapse in on itself, smaller and smaller, until it becomes a point of infinite density (which is a mind-blowing thing in itself). This is called a gravitational singularity. Most small stars (less than about 1.4 times the mass of our sun), will collapse into a dense, relatively cool star called a White Dwarf. Stars larger than this limit, which is called the Chandrasekhar limit, after the Indian astrophysicist who first calculated it, will collapse into some dense state like a black hole or neutron star.

Black holes suck in light because every object with a gravitational field has an escape velocity – that’s the speed you need to travel to break free from it’s gravity. Escape Velocity from Earth is about 25,000mph is needed. The escape velocity depends on the mass and the distance from the mass, so if the mass is big enough, then the escape velocity becomes larger than the speed of light. The distance from the black hole at which the escape velocity is equal to the speed of light is called the event horizon – beyond it light can never escape.